The Heart

Question 1

external anatomy of the heart

Answer 1

2 membrane coverings (paricardium)
-fibrous
-serous (2 layers)
heart wall (3 layers)
vessels entering/exiting
coronary arteries

Question 2

marginal artery supplies…

Answer 2

apex

Question 3

similarities between cardiac and skeletal mechanism of contraction

Answer 3

striated
-myosin/actin mechanism
t-tubule mechanism
-acting on sarcoplasmic reticulum

Question 4

differences between cardiac and skeletal mechanism of contraction

Answer 4

t-tubule mechanism - direct diffusion of Ca++
-tubules store larger amounts of Ca++
action potential
-cardiac muscle “plateau”
-plateau results in much longer time of contraction than skeletal muscle
strength of contraction
-dependent on extracellular Ca++

Question 5

ability of cardiac muscle to depolarize and contract is…

Answer 5

intrinsic

Question 6

heart’s intrinsic conduction system components

Answer 6

sinus node = sinoatrial/S-A node
internodal pathways
A-V node
A-V bundle
left and right bundle branches of Purkinje fibers

Question 7

features of SA node

Answer 7

smaller diameter muscle fibers
almost no contractile muscle fibers
connect directly with atrial muscle (mm) fibers
cell membranes naturally “leaky” to Na+ and Ca++ ions
-results in less negative resting membrane potential than other cardiac muscle cells
self-excitation

Question 8

how does EKG work (very broad)

Answer 8

electrical impulses passing through the heart also spread into adjacent tissues and some to the surface of the body
can be captured at surface of the body using electrodes

Question 9

what is the cardiac cycle

-what events are of note

Answer 9

events that occur from the beginning of one heartbeat to the beginning of the next
events
-chamber and vessel blood volume changes
-chamber and vessel blood pressures changes
-electrical activity noted
-heart sounds occur
-valves open and close

Question 10

cardiac cycle consists of what periods?

Answer 10

diastole
-period or relaxation; heart filling with blood
systole
-contraction period; heart ejects blood

Question 11

EDV and ESV values

Answer 11

EDV
-110-120 mL at rest
ESV
-40-50 mL

Question 12

what is isovolumic relaxation

Answer 12

ventricle is relaxing and the SL valve has closed, but the AV valve has not yet opened so blood cannot rush in

Question 13

what is isovolumic contraction

Answer 13

ventricle is contracting, but AV and SL valves are closed, so pressure is building without a change in volume

Question 14

relationship of cardiac cycle to ECG

• P
• QRS
• T

Answer 14

P: spread of depolarization through atrial tissue followed by contraction
-increases atrial pressure
QRS complex: spread of depolarization through ventricular tissue followed by contraction
-increases ventricular pressure
T wave: repolarization of the ventricles which represents ventricular relaxation

Question 15

atria function as “pumps”

Answer 15

atrial contraction usually causes an additional 20% ventricle filling; “primer pump”
atrial function “unnecessary” except during vigorous exercise

Question 16

atrial pressure changes

Answer 16

a wave
-during atrial contraction
c wave
-onset of ventricular contraction
v wave
-end of ventricular contraction

Question 17

preload

Answer 17

end-diastolic pressure when the ventricle is filled

-amount of tension on the muscle when it begins to contract

Question 18

afterload

Answer 18

pressure in the artery leading from the ventricle

load against which the muscle exerts its contractile force

Question 19

energy requirements for cardiac contraction

Answer 19

almost exclusive reliance on O2 for metabolism
70-90% from metabolism of fatty acids
10-30% from lactate, glucose
can use lactic acid generated by skeletal muscle activity

Question 20

heart pumps ____ of blood/minute

Answer 20

4-6 liters

Question 21

blood volume pump regulated by

Answer 21

intrinsic cardiac regulation of pumping in response to changes in volume of blood flowing into the heart
control of heart rate and strength of heart pumping by the autonomic nervous system

Question 22

Frank-Starling Mechanism

Answer 22

heart automatically pumps incoming blood
as cardiac muscle is stretched with returning blood volume, approach optimal length of actin and myosin fibers for contraction

Question 23

extrinsic regulation of the cardiac pump

-SNS

Answer 23

norepinephrine released by sympathetic nerve fibers in response to stressors such as fright, anxiety, or exercise; threshold reached more quickly

• increase CO
• -pacemaker fires more rapidly
• -enhanced muscle contractility

Question 24

extrinsic regulation of the cardiac pump

-PSNS

Answer 24

reduces HR when stressors removed
acetylcholine hyperpolarizes membranes of cells
-opens K+ channels
-PNS fibers in vagus nerves to heart can decrease CO
–primarily affects HR rather than contractility

Question 25

SNS and PSNS effects on heart during resting conditions

Answer 25

SA node receives impulses from both autonomic divisions continuously
dominant influence is inhibitory - heart said to exhibit “vagal tone”
“disconnect” vagal nerves = HR increase of 25 bpm